Safety devices for lifting appliances



Feb. 20, 1962 A. A. MEDAWAR 3,021,918

SAFETY DEVICES FOR LIFTING APPLIANCES Filed June 23, 1959 2 Sheets-Sheet 1 ATTORNEYS Feb. 20, 1962 A. A. MEDAWAR 3,0

SAFETY DEVICES FOR LIFTING APPLIANCES Filed June 25, 1959 2 Sheets-Sheet 2 I I 0 x w i 3 u.

l INVENTOR monwmawm ATTORNEY United States Patent SAFETY DEVICES FOR LIFTING APPLIANCES Andr Antoine Medawar, Luxembourg-Schleifmuhl,

France Ste. Congolaise Bunge Boite Postale 620,

Leopoldville, Belgian Congo) Filed June 23, 1959, Ser. No. 822,356 Claims priority, application Luxembourg July 5, 1958 7 Claims. (Cl. 182-112) This invention relates to an automatic safety device which can be used for all types of lifting appliances but is quite independent thereof. The object of the device is to prevent the load falling when something goes wrong with the actual lifting device or when the carrying rope breaks.

Certain devices known at the present time are so complicated that their functioning is not always certain; moreover they are often too heavy or too expensive. Other such devices have the disadvantage that they do not operate automatically and are therefore subject to forgetfulness or negligence on the part of the operator.

The device according to the invention uses for its movement during the raising of the load the thrust'of the lifting appliance properly so-called which, acting directly or indirectly, causes a pair of jaws to open automatically. In the stationary position or during the descent the jaws are closed, the tightening thereof being started by any force (such as a spring, hydraulic or pneumatic system, counterbalance, etc.), and then completed by the action of the load itself on the rope, acting by friction on the system of selftightening jaws and urging them towards the closed position.

In the accompanying drawings are shown some examples of application of the invention, which are not intended to limit the scope of the latter or exclude modifications.

FIGURE 1 is a diagrammatic view in elevation of the device, the rope being in a free position with the jaws FIGURE 2 is a corresponding transverse view.

FIGURE 3 shows the rope clamped by the jaws; half of the two cams and one jaw has been cut away to show the appliance better. In this position the safety device is locked and cannot move in either direction even if the load is reduced to zero.

FIGURE 4 shows the safety device according to the invention combined with a lifting appliance for a flying brid e.

FfGURE 5 shows a modification of the appliance shown in FIGURE 4.

Referring now to FIGURES 1 to 3, the rope 1 passes between the jaws 2 and 3 supported by means of their semi-cylindrical journals 4 by cams 5, 6, 7 and 8 (FIG- URES 1 and 2) pivoting about pins 9 and 10 fixed to the frame 11. The spring 12 maintains the cams and consequently the jaws in the tightening position (FIGURE 3), so long as no traction is exerted on the lever 13 in the direction of the arrow (FIGURE 1). The opening of the jaws during the ascending movement is brought about, in the example illustrated, by the thrust of the lifting appliance 14 on the nose 15 acting as an abutment (FIG- URE 3). This thrust on the cams via their pivot pins 9 and 10 which are fixed to the frame moves the jaws in the opening direction and so loosens them.

Opening of the jaws to insert the rope or to move the device along the rope during a descending operation, is effected by acting on the lever 13 in the opposite direction to that of the action of the spring 12.

The opposed pairs of jaws 2 and 3 are respectively journaled in the cams 5 and 6 in such a manner that in the downward position of the cams 5 and 6 as shown in FIG. 1, the opposed jaws are moved away from the cable.

This is due to the fact that the axes of the journals 4, 4 of each pair of opposed jaws are vertically spaced from each other, that is, the axes are not in alinement with each other and the axes 9 and 10 of the cams.

The manner in which the opposed jaws move toward and from each other as the cams 5, 6 are rotated can be explained by assuming a line drawn from axis 9 to the axis of upper journal 4 shown in full lines in FIG. 3. As the cam 5 is moved downwardly to the position of FIG. 1 it can be seen that the axis of this journal moves along an arc having its center on the axis 9 and recedes from the adjacent surface of the cable. If a line is drawn through the axis of the upper journal 4 shown in dotted lines in FIG. 3, rotation of cam 5 downwardly from the position shown in FIG. 3 to that shown in FIG. 1 will cause the axis of that journal to move along an arc which recedes from the adjacent surface of the cable. Since the jaws are secured to the journals, they will be moved away from the rope surface to reduce their friction thereon when the cams 5 and 6 are moved downwardly.

Referring to FIGURE 4, showing the combination of the device with a flying bridge or scaffold lifting appliance, the two devices 16 and 17 are mounted on the same ropes 18 and 19 as the two lifting appliances 20 and 21. Each safety device is however attached directly to the bridge or scaffold 22 by means of a sling 23. In the event of failure of the lifting appliance, the bridge remains connected to the safety device; the bridge is suspended on the lifting appliances by slings 18a and 19a.

FIGURE 5 shows a modification of the same application. In this case, each safety device slides on a rope 24, 25 respectively. The two ropes 24, 25 are parallel with the hoisting ropes and are fixed at their ends or are slightly taut. The devices 16 and 17 are solid with the bridge and in the event of failure of the lifting appliance or breaking of a hoisting rope at any point, the bridge is locked by the corresponding device on the parallel rope and is supported thereby at this end. This arrangement thus increases considerably the safety conditions of practical lifting. Naturally any other load can be provided in place of a flying bridge. Instead of a lateral supplementary rope, one could also use a bar or block of suitable length and diameter.

What I claim is:

1. A safety mechanism for a load member which is lifted and lowered by a load lifting member along a suspended tensioned cable comprising, a support device slidable on said cable, at least one pair of opposed jaws, means movably mounting the jaws on the support device, means constantly biasing said mounting means to move the jaws into frictional engagement with the cable, means connecting the load member to the support device, said jaws being so located on the movable mounting means that the cable, by reason of its engagement with the jaws, moves the jaws in the direction of their bias into tight clutching engagement therewith upon downward loading of the support device, said support device being movable upwardly by engagement with one of said members in its lifting movement while the jaws remain in slidable engagement with the cable.

2. A safety mechanism in accordance with claim 1, in which the load member is secured to the supporting device and the load lifting member comprises a second cable parallel with the tensioned cable and attached to the load member.

3. A safety mechanism in accordance with claim 1, in which the load lifting member comprises means in enacting engagement with the tensioned cable for lifting and lowering movement thereon and engageable with the support device during its lifting movement to move the support device upwardly, and means for attaching the load member to the load lifting member.

4. A safety mechanism in accordance with claim 1, including manually operable means for moving the jaw members out of engagement with the cable against their bias.

5. A safety mechanism in accordance with claim 1, in which the mounting means comprises at least one pair of horizontally spaced cam levers pivotally mounted at one end on a horizontal axis on the support device, the jaws being loosely journaled in said cam levers on opposite sides of the cable and about horizontal axis vertically spaced from each other.

6. A safety mechanism in accordance with claim 5 and including a spring between afixed location on the support and at least one cam lever, for biasing the lever to move the jaws into frictional engagement with the cable.

7. A safety mechanism for a load member which is lifted and lowered by a load lifting and lowering member along a suspended tensioned-cable comprising a support device slidable on said cable, jaw-carrying means movably mounted on the support device, a plurality of opposed-jaws movably mounted in the jaw-carrying'means, means constantly biasing said jaw-carrying means to move the jaws into frictional engagement with the cable, the mountings of the jaw-carrying means and jaws being such that frictional engagement of the cable with the jaws moves the jaw-carrying means in the direction of its bias to position the jaws into tight clutching engagement with the cable upon downward movement of the support device, and means attaching the load member to the support device, upward movement of the support device by one of the members causing the jaws to slip on the cable to allow lifting movement of the load.

References Cited in the file of this patent UNITED STATES PATENTS Puttre June 7, 1960 

